A utility-scale wind energy system or wind farm includes a group of wind turbines that operate collectively as a power plant to produce electrical energy without the consumption of fossil fuels. A wind turbine includes a rotor, a generator and a gearbox housed in a nacelle, and is placed on a tower at a sufficient height above the surrounding terrain so that the turbine is provided with wind currents which are stronger and more consistent than those at ground level. Megawatt class wind turbines can have nacelles weighing over 100 tons and rotors spanning over 90 meters. Because of their size, weight and operational height, performing major repairs on a wind turbine is costly, often requiring a crane to remove the rotor and nacelle from the tower. The major subassemblies of a wind turbine are therefore typically designed to have a service life span greater than or equal to the estimated service life of the wind turbine to reduce expected maintenance costs.
Rotors in a large wind turbine produce rotation with a low angular velocity and a high torque moment. To provide rotation having an angular velocity suitable for generating electricity with the generator, the gearbox may be required to provide overdrive ratios on the order of 100:1. Because epicyclic gears are capable of providing large overdrive ratios and high power transmission efficiency in a compact form factor, they are often employed for the input stages of gearboxes in wind turbine applications. The large torque moments applied to the input of the gearbox and the high overdrive ratios used to transfer power to the generator subject the moving parts of the gearbox to extreme forces. These forces may cause components to wear to the point of failure before the design lifespan of the wind turbine has elapsed.
In normal operation, each gearbox component produces a characteristic vibration, or vibration signature, from contact with neighboring gears, bearings, and other components in the gearbox. As the component wears, its vibration signature may be altered enough to determine when it is nearing the end of its service life. Likewise, a component failure may alter the vibration signature it produces sufficiently to allow immediate detection of the failure. Thus, one potential way to monitor gearbox component health is by detecting and analyzing the vibrations produced by the gearbox components so that abnormal vibrations can provide an early warning to wind turbine operators. However, the vibration transmission path from many of the internal components of the gearbox to the gearbox case is attenuated by passage through lubricants, across multiple gears and bearing mating surfaces, and through other components. Individual component vibration signatures detected from outside the gearbox are also masked by vibrations emitted by other components, making it difficult to isolate a single failure. The combination of attenuated signals and background noise levels thus reduce the ability of sensors mounted to the gearbox case to detect worn components early in the failure process.
Mounting vibration sensors in closer proximity to the component being monitored may create a more direct path for vibration energy transmission. This may increase signal to noise ratio to more reliably detect abnormal vibration emissions of an individual component sufficiently early in the failure process to allow preventative measures to be implemented, or to schedule repairs, before the predicted failure occurs. However, because of the confined space of an epicyclic gearbox, as well as the complex rotation and movements of the internal components, using wires or cables to recover signals from, and provide power to, sensors mounted to moving parts within a gearbox is impractical.
Accordingly, there is a need for improved systems and methods for monitoring the health of a wind turbine gearbox that allow sensors to accurately assess vibration signatures and to operate without cables or wires.